1. Field of the Invention
This invention relates to control valves and a method for their manufacture. More particularly, it concerns angle-type valves designed for use in controlling flow of highly erosive fluids, e.g., hot pitch, so constructed as to withstand severe erosive action within the valve.
2. Description of the Prior Art
Hot pitch discharged from coke ovens contains fine particles of highly abrasive material. The flow of such pitch must be controlled by valves in the course of its handling which involves its flow at relatively great velocity at high temperatures. Such conditions can cause flashing and cavitation within a control valve that materially contribute to the action of the abrasive particles in producing rapid erosion of valves that have been available for controlling flow of hot pitch or similar erosive fluids.
The problem of attack of valve parts by action of fluids passing through the valves has been addressed by the prior art in various ways. One solution has been to form parts for plug-type valves of ceramic material, rather than metal, e.g., see U.S. Pat. Nos. 867,780; 885,526 and 925,809. Another approach has been to use ball-type valves provided with plastic coatings to reduce the attack by fluids being handled, e.g., see U.S. Pat. Nos. 3,073,336 and 3,825,030. A further development for protection of valves against abrasive action was the use of tubular inserts of boron carbide in ball type valves, e.g., see U.S. Pat. No. 3,985,150.
It has also been known to use tubular inserts of corrosion resistant material, such as carbon, to reduce corrosion of angle-type valves designed to control flow of acid, e.g., see U.S. Pat. No. 2,792,845.
In spite of the many advances made in valve construction to reduce corrosion or erosion problems, the need exists for further improvements in control valves for use in regulating flow of highly abrasive fluids, particularly when such fluids are handled at high temperatures and flow rates.